Monitoring of overall building energy consumption with the ability to drill down to an individual electric appliance level is a desirable capability of Building Energy Management Systems (BEMS). Having the individual power consumptions of all (major) appliances substantially widens the possibilities and enables a number of new and useful functionalities, e.g. the performance monitoring of individual devices, fault detection and diagnostics, etc. Due to the large investment required for physical sub-meter installation (meters plus wiring and labor cost), NILM (Non-Invasive Load Monitoring) techniques have been receiving considerable attention in the research community for the past twenty years or so. These methods use just one meter that is placed somewhere in the building wiring hierarchy, and these meters estimate/disaggregate the power consumption of devices beyond this measurement point.
However, the results achievable with common instrumentation are not very reliable, and the advanced techniques promising higher reliability of the results still incur large costs (expensive proprietary hardware capable of fast sampling and digital signal processing). Low reliability is often caused by an algorithm's inability to distinguish among similar devices (e.g., several air-handling units of the same capacity from the same manufacturer). This is unfortunately very common in the commercial/public building environment.